144 0001055951 XXXXXXXX LIVE 0002036042 Sionna Therapeutics, Inc. 001-42504 21 HICKORY DRIVE SUITE 500 WALTHAM MA 02451 617-819-2020 OrbiMed Private Investments VIII, LP Shareholder Common Stock TD Cowen

599 Lexington Avenue New York NY 10022

1047770 46500032.60 44628788 11/24/2025 Nasdaq Stock Market Common Stock 02/10/2025 IPO Issuer N 1047770 02/10/2025 Cash Y OrbiMed Capital GP VIII LLC is the general partner of OrbiMed Private Investments VIII, LP. OrbiMed Advisors LLC is the managing member of OrbiMed Capital GP VIII LLC. 11/24/2025 02/10/2025 /s/ Douglas Coon, Chief Compliance Officer, OrbiMed Advisors LLC, managing member of the general partner of OrbiMed Private Investments VIII, LP